Painting with combined textures - select texture section to use
Your UV unwrapping needs to coincide with the image texture you are using. I would select the faces that need to be using a square of the image texture and Unwrap and then Reset, so that they are overlapped squares and with those selected in the UV Image Editor, scale and rotate to place them over the desired image portion - repeating the process until the unwrap is using the image the way you intend.